P1202: NOVEL METHODS FOR THE IDENTIFICATION OF A RARE DISEASE, HEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS (HLH)
Authors: Catherine M Broome, Meghan Mitchell, Lauren Bylsma, Nawar Shara, Stephen Fernandez, Joseph Catlett, Jacob Lai, Kathy Dong, Jon Fryzek, Naval Daver, Carl Allen
Journal: HemaSphere (2023)

Topic: 19. Aggressive Non-Hodgkin lymphoma - Clinical Background: Hemophagocytic lymphohistiocytosis (HLH) is a rare, acute, uncontrolled immune activation syndrome characterized by clinical evidence of extreme inflammation. While ICD codes are available for HLH-related conditions, identifying and diagnosing HLH is challenging due complex diagnostic criteria, a high mortality rate, and heterogeneous etiology and presentation. Aims: The objective of this study was to develop novel strategies to compile a retrospective cohort of HLH patients at a large US healthcare system. Methods: An Electronic Medical Record (EMR) system was queried 2009-May 2022 to identify potential patients. Three methods were developed for patient identification. Method 1 identified patients with any mention of an HLH-related ICD code (ICD-9 288.4; ICD-10 D76.1, D76.2, D76.3). Method 2 identified patients with elevated ferritin values (≥1,000 ng/mL or ≥10,000 ng/mL) or a sCD25 test (predictive markers of HLH). Method 3 identified patients with etoposide and dexamethasone treatment, removing patients receiving this treatment as part of a chemotherapy regimen. A clinician reviewed a random sample of patients identified by each method for HLH diagnosis. Results: Method 1 (N=327) was found to be predictive for HLH, with 17% of the random 20% sample confirmed HLH; all Method 1 patients were included for full chart review. The following cohorts within Method 2 (N=1,057) were found to be predictive of an HLH diagnosis and were included for full chart review: ferritin ≥10,000 ng/mL and any sCD25 test (N=42, 13% of patients in the 20% random sample confirmed HLH) and patients with ferritin 1,000-10,000 ng/mL and any sCD25 test (N=94, 17% of patients in the 20% random sample confirmed HLH). Random 10% sampling of the cohorts of patients with 1) any sCD25 test and no ferritin ≥1,000 ng/mL (N=374) and 2) ferritin ≥10,000 ng/mL and no sCD25 test (N=547) were found to have few patients with HLH (N=1 or 3% and N=1 or 2%, respectively). Since full chart review of these large cohorts was not logistically feasible, discharge summaries within these cohorts were screened for mentions of HLH or MAS resulting in 64 unique patients identified for full chart review. Chart review of a random 20% sample of patients within Method 3 (N=86) found no cases of HLH. One unique patient was identified from searching discharge summary notes of this patient population. After de-duplication, 528 unique patients were identified for full chart review to determine an HLH diagnosis. Results of this chart review will be presented. Summary/Conclusion: Our expanded algorithm captured a substantial number of patients that would have been missed with identification using ICD codes alone, indicating a potential underestimation of HLH incidence. Keywords: Hemophagocytic Lymphohistiocytosis (HLH), Macrophage Activation Syndrome (MAS)